In humans and animals, aging decreases dietary and energy requirements and it is generally believed that reduced consumption is related to alterations in taste preference. However, the mechanisms underlying an age-induced shift in taste preference remain unclear. The researchers investigated differences in fluid intake and taste nerve responses across different age groups of rats.

The researchers initially measured the intake of sweet, salty, umami, sour or bitter taste solutions in five age groups- juvenile, young-adult, adult, middle-aged and old-aged male rats. The results showed that older animals exhibited a decreased preference for sweet and umami taste and a reduced aversion to bitter taste.

To elucidate the neural mechanisms of such age-related changes in taste preference and sensitivity, electrophysiological experiments examined taste response characteristics of chorda tympani nerves. These nerves mediate gustatory information from the tongue to the brainstem. The researchers observed no significant differences in activity of the chorda tympani nerves by taste stimuli across the different age groups.

Overall, these behavioral and electrophysiological studies demonstrate that age-related changes in taste preference and sensitivity are independent of the peripheral gustatory system.

The lead author of the study, Chizuko Inui-Yamamoto, says, “To our knowledge, this is the first report demonstrating a reduced aversion to bitter taste in aged rats.” She comments, “We had expected that these changes were due to the peripheral taste system.”

However, differences in electrophysiological recording of taste responses of the chorda tympani nerves across age groups were not observed. “Our studies showed that aging elicited no changes in transmission of taste information from the tongue to the central nervous system. Thus, our future work will investigate the role of the central nervous system in mediating age-induced changes in taste preference”, says Inui-Yamamoto.

This work was supported by JSPS KAKENHI Grant-in-Aid for Young Scientists.